In cardiology, more particularly electrophysiology, two or more catheters are introduced through the vascular system into the heart in order to carry out diagnosis and/or therapy therein. Since relatively large spaces are present in the heart compared to the vessels, the problem arises of navigating the catheters accurately to the desired destination in these spaces and to keep track of their location. In certain cases it is necessary to determine the exact position of a catheter in the space with absolute precision, for example in order to use said position for imaging representations.